how to make all field optional with alias name?

I am following https://stackoverflow.com/a/77851176/243031 to create my model optional.

I created function to get base class annotations.

def get_annotations(main_cls):
    ret_val = main_cls.__annotations__
    for base_cls in main_cls.__bases__:
        if base_cls != BaseModel:
            ret_val.update(get_annotations(base_cls))
    return ret_val

and created optional model as

OptionalClientModel = create_model(
    "OptionalClientModel",
    **{k: (Optional[v], None) for k, v in get_annotations(ClientModel).items()})

The original classes are as below

from typing import Annotated
from bson import ObjectId

from pydantic import Field
from pydantic import EmailStr
from pydantic import BaseModel
from pydantic import BeforeValidator
from pydantic import ConfigDict
from pydantic import AwareDatetime
from pydantic import field_validator

# Represents an ObjectId field in the database.
# It will be represented as a `str` on the model so that it can
# be serialized to JSON.
PyObjectId = Annotated[str, BeforeValidator(str)]

class DBTableBase(BaseModel):
    # The primary key for the Table, stored as a `str` on the instance.
    # This will be aliased to `_id` when sent to MongoDB,
    # but provided as `id` in the API requests and responses.
    id: PyObjectId | None = Field(alias="_id",
                                  serialization_alias="id",
                                  default=None)
    model_config = ConfigDict(
        json_encoders={ObjectId: str},
        json_schema_extra={
            "example": {
                "id": "BSON_ID"
            }
        },
    )

class ClientModel(DBTableBase):
    first_name: str
    last_name: str

When I want model with all optional value, I can use OptionalClientModel.

The issue is, id in OptionalClientModel has no alias.

How to create optional with alias?

Solution

With the following approach you can pass the FieldInfo objects from the original model to the new dynamically created model while giving the annotation an extra | None.

OptionalClientModel = create_model(
    "OptionalClientModel",
    **{k: (v.annotation | None, v) for k, v in ClientModel.model_fields.items()})

Edit: To set a default value of None as well you have to mutate the FieldInfo object before passing them to the create_model function. You also may have to copy the FieldInfo object on beforehand. Normally it wouldn't change anything but I am almost sure (didn't test it) that if you are calling model_rebuild on the original model somewhere the changes on the FieldInfo objects will be reflected on the rebuilt pydantic core schema.

field_infos = {}
for field_name, field_info in ClientModel.model_fields.items():
    field_info_copy = copy(field_info)
    field_info_copy.default = None
    field_infos[field_name] = field_info_copy

OptionalClientModel = create_model(
    "OptionalClientModel", **{k: (v.annotation | None, v) for k, v in field_infos.items()}
)